1. Field of the Invention
This invention relates to a cylinder type air damper and, more particularly, to an air damper for providing a braking force which is variable according to the load applied thereto.
2. Description of the Prior Art
Air dampers of this type generally comprise a cylinder, a piston inserted for reciprocation within the cylinder and axially dividing the interior of the cylinder into front and rear compartments, an orifice axially penetrating the piston for permitting the exchange of air between the two compartments in response to axial movement of the piston, and an exhaust hole axially penetrating the piston and provided with a valve for preventing the exchange of air between the two compartments in response to the axial movement of the piston in one direction, as disclosed in Japanese Utility Model Publication SHO 62-24845, Japanese Utility Model Public Disclosure SHO 63-190946, U.S. Pat. No. 4,796,732 and U.S. Pat. No. 4,856,625.
However, the above prior art air dampers have a problem in that the speed of the piston varies with a change in the load exerted upon the air damper.
Since the orifice diameter is fixed, the piston speed is increased with an increasing load impressed upon the damper. For instance, when this damper is used in connection with a door pivoted downwardly about a shaft disposed at the lower end of the door when it is opened, such as, for example, the door of an automobile glove compartment or the like, such that its braking force is utilized when the door is pivoted downwardly, the load exerted upon the damper increases as the door is pivoted downwardly. Therefore, the door opening speed is initially low and accelerates as the door approaches the end of the opening movement.